This invention relates to the field of semiconductor devices, and particularly to Junction Field Effect Transistor structures for use in materials with low electron mobility and high saturation velocities.
There has been a long felt need to provide semiconductor devices capable of operating in severe environments. .beta. silicon carbide has a wide bandgap of 2.2 eV, a high theoretical saturated electron drift velocity of 2.times.10; cm/s, a high breakdown field of 5.times.10.sup.6 V/cm, and a high thermal conductivity of 3.5 W/cm.multidot..degree.C. Silicon carbide is also relatively chemically inert and thermally stable. These properties combine to make .beta. silicon carbide an attractive material for high-temperature and high-power device applications.
Unfortunately, Silicon Carbide semiconductors have heretofore had a limited frequency range due to the low electron mobility of Silicon Carbide. Low mobility can normally be corrected in field effect transistors by reducing the gate length. However, because of the rudimentary fabrication technology available for silicon carbide, it is difficult to fabricate the necessary sub-micron gate lengths in silicon carbide. While these dimensions can be achieved by use of electron beam lithography, they are beyond the capability of conventional mass production processes using optical photo-lithography.